Probably not harmful, just mushrooms. Mushrooms are the surface, fruiting part of subterranean fungus. Such fungus can be beneficial, mychorrhiza is symbiotic and colonizes tree roots, evergreens in particular. http://en.wikipedia.org/wiki/Mycorrhiza
I get them sometimes with my oak bonsai. Never seen mushrooms this yellow though...]
Unless the plant looks stressed now or in the coming weeks, I wouldn't worry about it.
I think the yellow color is from what ever lighting was used to take the photo.
If those things are white keep your kids away from them. That looks very much like a mushroom called "Death Angel". It gets it's name from how quickly someone dies if they take one bite of it. You see them pop up in the woods a lot around here. They will be pure white and then slowly turn brown as they wilt down. Don't let the kids taste them.
Thanks for all the replies. Mac, they are definately yellow. Very nice color actually. I think I will just repot into a mixthat I have been using for my other Junipers. The soil in there now is what it came in and yes,, it is wet most of the time.I will watch that alot better from now on. Thanks everyone!! Joe
It's not a destroying angel mushroom but it is mildly toxic. That is a common lepiota lutea mushroom. It's not deadly at all. people tend to overreact when they see fungi and start naming death caps and destroying angels.
Most mushrooms growing in our pots are a sign of health, and often have a symbiotic relationship with the trees, helping eachother grow. However, there are certain parasitic fungi that can harm our trees, and if left untreated can even kill them (there are very few of these though). Enjoy your little treasures, mycology is a very interesting field of study.